Apparatus and method for transmitting data using a plurality of carriers

ABSTRACT

An apparatus for receiving signals includes a receiver for receiving a time domain signal from a transmitter, wherein at least one first information bit is mapped, resulting in at least one first mapped symbol; at least one second information bit is mapped, resulting in at least one second mapped symbol; the at least one second mapped symbol is multiplied by at least one third information bit; and the time domain signal is generated from the at least one first mapped symbol and the at least one second mapped symbol.

This application is a Continuation of U.S. application Ser. No.14/491,307 filed Sep. 19, 2014, which is a Continuation of U.S.application Ser. No. 13/725,204 filed Dec. 21, 2012 (now U.S. Pat. No.8,873,658), which is a Continuation of U.S. patent application Ser. No.13/278,135, filed Oct. 20, 2011 (now U.S. Pat. No. 8,340,203), which isa Continuation of U.S. application Ser. No. 12/096,565, filed on Oct. 6,2008 (now U.S. Pat. No. 8,059,738), which is a National Stage under 35U.S.C. 371 of International Application No. PCT/KR2006/005234, filedDec. 6, 2006, which claims the benefit of earlier filing date and rightof priority to Korean Patent Application Nos. 10-2005-0118200, filedDec. 6, 2005 and 10-2005-0124709, filed on Dec. 16, 2005, all of whichare hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The invention relates to a method of transmitting and receiving data ina communication system, and more particularly, to a data transmittingand receiving method of transmitting supplementary data in acommunication system based on an orthogonal frequency divisionmultiplexing (hereinafter, referred to ‘OFDM’).

BACKGROUND ART

Recently, demand for high-speed data transfer is increasing, and theOFDM suits with this high-speed data transfer and is employed in varioushigh-speed communication systems. Hereinafter, the OFDM will bedescribed. A basic principle of the OFDM is that a data stream having ahigh-rate is divided into a plurality of data streams having a slow-ratethat are transmitted by a plurality of carriers simultaneously. Each ofthe plural carriers is called a sub-carrier. Since there isorthogonality between the plural carriers of the OFDM, a frequencycomponent of the carrier can be detected at a receiving end even whenthe carriers are overlapped with each other. The data stream having ahigh-rate is transmitted to the receiving end by which the data streamis converted into a plurality of data streams having a low-rate by aserial-to-parallel converter, the sub-carriers are multiplied to theparallel converted plural data stream, and the multiplied converted datastreams are combined with each other.

An orthogonal frequency division multiple access (OFDMA) is a multipleaccess method of allocating the sub-carriers to entire broadband in theOFDM according to transfer rate demanded by multiple users.

There is proposed a single carrier frequency division multiple access(SC-FDMA) technique of adding a spreading technique by a discreteFourier transform (DFT) spreading matrix to the OFDM technique. TheSC-FDMA technique has a low Peak-To-Average Power Ratio (PAPR).

The OFDM communication technique is a communication method used invarious systems such as IEEE 802.11a/g, HiperLAN, IEEE 802.16, DigitalSubscriber Line (DSL), Digital Audio Broadcasting (DAB), Digital VideoBroadcasting (DVB), and the like and is effective when a communicationchannel appears as a selective-fading phenomenon. The OFDM communicationmethod uses several sub-carriers so that the selective-fading looks likea flat fading and has a merit that a technique of compensating thefading is simplified in overall system. In order to easily estimate thesimplified channel, pilot sub-carrier information is used. Since aposition and a value of the pilot sub-carrier are already known to atransmitting end and a receiving end, the receiving end can obtain theposition and value of the pilot sub-carrier simply by carrying outdivision (or equivalent operation) in order to estimate the channel.

For the synchronization, a phase difference between different OFDMsymbols is determined, and this is obtained by comparing a phase of apilot signal with the different OFDM signals.

This pilot may be used in various purposes other than theabove-mentioned two purposes, for example, in an encoded pilot or in atechnique of reducing the PAPR.

FIG. 1A illustrates a conventional transmitting end to transmit an OFDMsignal. As illustrated in the drawing, data bits are mapped intospecific data symbols according to constellation mapping, and pilot bitsare mapped into specific pilot symbols according to constellationmapping. The data symbol is mapped into sub-carriers after beingconverted into a parallel signal (a transfer symbol to be transmitted tothe receiving end) through the serial-to-parallel conversion. The datasymbol is transmitted to the receiving end after carrying out aninversion fast Fourier transform (IFFT). The data bits represent a bitstream indicating user data except for the pilot sub-carrier.

The operation is expressed by the formulas as follows.

In the conventional OFDM transfer technique, when N sub-carriers areused, N_(p) pilot sub-carriers among the N sub-carriers are allocatedand the rest is allocated to data or a guard band. Hereinafter, for theillustrative convenience, the data (the user data and the pilot data)except for the guard band will be described. When the number of thesub-carriers allocated to the data is N_(d), a relationshipN=N_(p)+N_(d) is established. A vector of the transfer symbol in whichthe user data is combined with the pilot signal,

=[S₀, S₁, Λ, S_(N-1)]^(T) is expressed by the following formula.

=P _(d)

+P _(p)

  [Formula 1]where, Pd and Pp are matrixes of re-arranging the user data and thepilot sub-carriers at positions of the already allocated sub-carriers,and the

and

are the symbol vectors transmitted by the user data and the pilotsub-carriers respectively and the lengths thereof are N_(d) and N_(p)respectively. The transfer symbol vector

in the frequency region meets with the IFFT like in the followingformula.

=[x ₀ ,x ₁ ,Λ,x _(N-1)]^(T) =F ⁻¹

  [Formula 2]

where, F is a Fourier transform matrix. The vector

is modulated into a carrier frequency to be transmitted through anantenna again, and the receiving end receives a signal such as

=

+

Here,

is a response vector of a wired/wireless channel and

corresponds to a noise. The receiving end firstly carries out theFourier transform in order to demodulate the vector

representing the receiving signal. Then, the following formula 3 isexpressed.

=F

=H

+F

  [Formula 3a]

where, H represents a channel response within the frequency region and

represents original data. If the channel has been estimated, thetransfer signal is demodulated by the following formula according to theestimated channel value.

=(H ^(H) H)⁻¹ H ^(H)

  [Formula 3b]

where,

is an estimated value of

. A conventional method of transmitting the OFDM signals is identical tothe above-mentioned transfer method or is carried out by processescorresponding to the same.

Hereinafter, the PAPR causing a problem in the OFDM communication systemwill be described.

In the OFDM communication system, there occurs a problem such that alinear span of a power amplifier of an transmitting end must be wider asthe PAPR is high. In general, since a power amplifier having a largelinear span is expensive, in order to reduce manufacturing costs ofmobile terminals, a cheap power amplifier is used in wired/wirelesscommunication so that an output range is narrow and due to this, theOFDM signal is distorted.

Various methods have been proposed in order to solve the problems aboutthe PAPR, and are grouped into two parts. A first method is to transmitadditional information for PAPR identification (for example, a selectivemapping, a partial transmit sequence, and the like), and transmit theadditional information for PAPR identification through an additionalchannel by forming the additional channel in a way of using some of thesub-carriers. A second method does not need the additional informationfor PAPR identification (for example, a tone reservation), and in thiscase, the user consumes more electric power and a receiving endundergoes more interference.

FIG. 1B is a view illustrating a conventional transmitting end to reducethe PAPR using the additional information for PAPR identification.

In the conventional transmitting end illustrated in FIG. 1B, the OFDMsignal is transmitted according to the formulas 1 and 2.

A PAPR reducing technique has a target of minimizing a differencebetween an average value and a maximal value of power of

in Formula 2. The PAPR is defined by the following formula.

$\begin{matrix}{{PAPR} = \frac{\max\limits_{{k - 0},\Lambda,{N - 1}}{x_{k}}^{2}}{\frac{1}{N}{\sum\limits_{k = 0}^{N - 1}{x_{k}}^{2}}}} & \left\lbrack {{Formula}\mspace{14mu} 4a} \right\rbrack\end{matrix}$

As shown in the above formula, when any one of the vector components hasan abnormally large value, the PAPR is increased and the characteristicof the signal is deteriorated. To solve this problem, a method used inthe frequency region can be expressed by the following formula.

=M _(s) M _(p)

  [Formula 4b]

where, Ms is a matrix of varying a phase component of the respectivedata components of

and M_(p) is a matrix of changing order of the data components. This newmodified data vector

is transformed into a signal in a time domain through a transform suchas the formula 2 and the PAPR of a signal transformed into the timedomain.

Since there are several M_(s) and M_(p), signals are made in a timedomain and the smallest PAPR is selected from the signals and istransmitted. At that time, the additional information about the M_(s)and M_(p) must be transmitted and this information is called theadditional information for PAPR identification.

The additional information for PAPR identification can be transmitted bygenerating additional channel in a code division multiple access (CDMA)communication system. The OFDM communication system adopts a method ofbeing allocated with some of the sub-carriers to transmit the additionalinformation for PAPR identification.

The conventional methods of transmitting the additional information forPAPR identification must use the additional channel for the transmissionof the additional information for PAPR identification.

If some of the sub-carriers of the OFDM communication system are used asthe additional channels, the communication system may be deteriorated.

Moreover, in the conventional methods of not transmitting the additionalinformation for PAPR identification, the transmitting end's total poweris increased and interferes with other receiving ends.

DISCLOSURE OF INVENTION

Therefore, the present invention has been made in view of the aboveproblems, and it is an aspect of the present invention to provide anorthogonal frequency division multiplexing signal transmitting andreceiving method of generating a new channel for data communication.

It is another aspect of the present invention to provide an informationtransmitting and receiving method of reducing a peak-to-average ratio(PAPR) through a new generated channel for data communication.

In accordance with an aspect of the present invention, the above andother objects can be accomplished by the provision of a method oftransmitting an orthogonal frequency division multiplexing signalcomprising: mapping an input bit stream into at least one transfersymbol; changing at least one of amplitudes and phases of the transfersymbols that are transmitted by a specific sub-carrier group having aplurality of sub-carriers using constellation modification informationto indicate specific additional data; and transmitting the transfersymbols, to which the changing is carried out, to a receiving end by anorthogonal frequency division multiplexing data processing, theconstellation modification information being identical to each otherwith respect to the transfer symbols that are transmitted by thespecific sub-carrier group.

In accordance with an aspect of the present invention, the above andother objects can be accomplished by the provision of an orthogonalfrequency division multiplexing signal transmitting apparatus totransmit a data symbol to a receiving end using a plurality ofsub-carriers, the transmitting apparatus comprising: a first mappingmodule to map an input bit stream into at least one transfer symbol; anda second mapping module to change at least one of amplitudes and phasesof the transfer symbols that are transmitted by a specific sub-carriergroup having a plurality of sub-carriers, using constellationmodification information to indicate specific additional data bychanging the at least one of the amplitudes and the phases of thetransfer symbols that are transmitted by the specific sub-carrier groupusing constellation modification information identical to each other.

In accordance with an aspect of the present invention, the above andother objects can be accomplished by the provision of a method ofreceiving an orthogonal frequency division multiplexing signaltransmitted by a plurality of sub-carriers, comprising: estimating atleast one of amplitudes and phases of receiving symbols received by theplurality of sub-carriers by estimating at least one of modifiedamplitudes and phases from previously determined amplitudes and phases;acquiring additional data to indicate at least one of the estimatedamplitudes and phases; recovering the amplitudes and phases of thereceiving symbols using at least one of the estimated amplitudes andphases; and acquiring data contained in the recovered receiving symbols.

In accordance with an aspect of the present invention, the above andother objects can be accomplished by the provision of a receiving end toreceive an orthogonal frequency division multiplexing signal transmittedby a plurality of sub-carriers, comprising: a first demodulating moduleto estimate at least one of amplitudes and phases of receiving symbolsreceived by the plurality of sub-carriers by estimating at least one ofmodified amplitudes and phases from previously determined amplitudes andphases, and to acquire additional data to indicate at least one of theestimated amplitudes and phases; and a second demodulating module torecover the amplitudes and phases of the receiving symbols using atleast one of the estimated amplitudes and phases, and to acquire datacontained in the recovered receiving symbols.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1A illustrates a conventional transmitting end to transmit anorthogonal frequency division multiplexing (OFDM) signal;

FIG. 1B is a view illustrating a conventional transmitting end to reducea peak-to-average power ratio (PAPR) using additional information forPAPR identification;

FIG. 2 is a view illustrating an example of a transmitting end oftransmitting additional data, contained in a pilot signal, according toan embodiment of the present invention;

FIG. 3 is a view illustrating an example of a transmitting end oftransmitting additional data, contained in a data signal, according toan embodiment of the present invention;

FIG. 4 is a view illustrating a receiving end of receiving a receivingsignal, containing additional data signal, according to an embodiment ofthe present invention;

FIG. 5 is a view illustrating a constellation map of data in which amacro constellation mapping is carried out by a binary phase shiftkeying (BPSK) and a micro constellation is carried out;

FIG. 6A illustrates a phase range that a micro constellation coordinatemay have when the macro constellation mapping is the BPSK;

FIG. 6B illustrates a range of a value that the micro constellationcoordinate may have when the macro constellation mapping is an M-aryquadrature amplitude modulation (QAM);

FIG. 7 is a view illustrating a result that the micro constellationcoordinate is generated when the macro constellation mapping is theBPSK;

FIG. 8 is a view illustrating a result that the micro constellationcoordinate is generated when the macro constellation mapping is theM-ary QAM;

FIG. 9 is a view illustrating a concept of a method of transmitting databy containing additional data in the data according to an embodiment ofthe present invention;

FIG. 10 is a view illustrating a maximum value of the additional data tobe contained in a pilot signal and to be transmitted in the embodimentof the present invention;

FIG. 11 is a view illustrating an error ratio with respect to theadditional data when the additional data is contained in the pilotsignal to be transmitted in the embodiment of the present invention;

FIG. 12 is a view illustrating an error ratio of phase estimation withrespect to a micro constellation signal when the additional data iscontained in the pilot signal to be transmitted in the embodiment of thepresent invention;

FIG. 13 is a view illustrating an error ratio with respect to theadditional data when the additional data is contained in a data signalto be transmitted in the embodiment of the present invention;

FIG. 14 is a view illustrating an error ratio of phase estimation withrespect to the micro constellation signal when the additional data iscontained in the data signal to be transmitted in the embodiment of thepresent invention;

FIG. 15 is a view illustrating an example of an OFDM signal transmittingend to reduce PAPR according to an embodiment of the present invention;

FIG. 16 is a view illustrating an example of a phase mapper according toan embodiment of the present invention;

FIG. 17A is a view illustrating a method of selecting a value of φ_(k)^(m) when the macro constellation mapping is the M-ary QAM;

FIG. 17B is a view illustrating a method of selecting a value of φ_(k)^(m) when the macro constellation mapping is the BPSK;

FIG. 18 illustrates configuration of a receiving end according to anembodiment of the present invention;

FIG. 19A is a view illustrating an example of a phase demapper accordingto an embodiment of the present invention;

FIG. 19B is a view illustrating another example of the phase demapperaccording to an embodiment of the present invention;

FIG. 20 is a view illustrating performance when a data transmitting andreceiving method according to an embodiment of the present invention isused; and

FIG. 21 is another view illustrating the performance when a datatransmitting and receiving method according to an embodiment of thepresent invention is used.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings.

The present invention proposes a method of containing additional datagenerated by a micro constellation mapping into a pilot signal or a userdata signal that is transmitted by specific sub-carriers.

The micro constellation mapping method is distinguished from aconstellation mapping method applied to the pilot signal or the datasignal that is contained in an orthogonal frequency divisionmultiplexing (OFDM) symbol, and a additional channel can be generated bycarrying out the micro constellation mapping in the present invention.In the present invention, the additional data is transmitted by themicro constellation mapping so that it is not necessary to notifycontrol information for the recovery of the additional data to areceiving end.

Structure, operation, and effect of the present invention will bedescribed in detail through the following embodiments of the presentinvention.

A first embodiment of the present invention relates to a method offorming a new data channel in a conventional OFDM communication system(for example, the OFDM communication system, the orthogonal frequencydivision multiple access (OFDMA) communication system, and a singlecarrier frequency division multiple access (SC-FDMA) communicationsystem).

Through the new data channel, a variety of additional information can betransmitted and received. In a second embodiment of the presentinvention, a method of transmitting information for a peak-to-averagepower ratio (PAPR) utilizing the first embodiment of the presentinvention will be proposed. In other words, the micro constellationmapping (or, a phase shift) is carried out according to the firstembodiment of the present invention, and information for the PAPR istransmitted and received by carrying out the micro constellationmapping.

Hereinafter, the first embodiment of the present invention will bedescribed.

Embodiment 1

In the first embodiment of the present invention, data is transmitted byoverwriting a separate constellation signal for additional data onto agroup of sub-carriers in the OFDM communication system, and anadditional control signal that a receiving end uses to correctly recoverthe overwritten constellation signal is not transmitted.

The first embodiment of the present invention provides roughly twomethods, such as a method of transmitting and receiving additional databy containing the additional data in the user data signal included in anOFDM symbol, and a method of transmitting and receiving additional databy containing the additional data in the pilot signal included in anOFDM symbol.Moreover, the transmitting and receiving method of containing theadditional data in the user data signal is divided into a method oftransmitting and receiving the additional data by containing theidentical additional data in all user data signals contained in a singleOFDM symbol and a method of transmitting and receiving the additionaldata by containing different additional data in respective groups inwhich data signals, included in a single OFDM symbol, are grouped.

FIG. 2 is a view illustrating an example of a transmitting end oftransmitting the additional data, contained in the pilot signal,according to the first embodiment of the present invention. Moreover,FIG. 3 is a view illustrating an example of a transmitting end oftransmitting the additional data, contained in the data signal,according to the first embodiment of the present invention. Hereinafter,the method of transmitting data according to the first embodiment of thepresent invention will be described with reference to FIGS. 2 and 3.

The transmitting end in FIG. 2 includes a macro constellation mappingmodule 210 to carry out a constellation mapping of user data bits, amacro constellation mapping module 220 to carry out a constellationmapping of pilot bits, a micro constellation mapping module 230 to carryout a constellation mapping of additional data bits that are transmittedtogether with the pilot bit, a serial-to-parallel (S/P) converter 240 toconvert transfer symbols into parallel signals, a multiplexer (MUX) 250to allocate the parallel signals to the sub-carriers, an N pointinversion fast Fourier transform (IFFT) module 260 to perform a IFFToperation, and a parallel-to-serial (P/S) converter 270 to convert theparallel signals into serial signals to transmit the converted serialsignals to a radio frequency (RF) module of the transmitting end.

The transmitting end in FIG. 3 includes a macro constellation mappingmodule 310 to carry out a constellation mapping of user data bits, amacro constellation mapping module 320 to carry out a constellationmapping of additional data bits that are transmitted together with theuser data, a macro constellation mapping module 330 to carry out aconstellation mapping of pilot bits, a S/P converter 340 to converttransfer symbols into parallel signals, a MUX 350 to allocate theparallel signals to the sub-carriers according to a predetermined rule,an N point IFFT module 360 to perform a IFFT operation and a P/Sconverter 370 to convert the parallel signals into serial signals totransmit the converted serial signal to an RF end of the transmittingend.

The user data bits mean bits representing the user data signal to betransmitted in the OFDM system, the pilot bits mean bits representingthe pilot signals, already known to a transmitting end and a receivingend, and the additional data bits mean the additional data signals to beadditionally transmitted in the present invention. The macroconstellation mapping means a constellation mapping method with respectto the user data signals and the pilot signals except for the additionaldata signals. Thus, the macro constellation mapping is enabled by abinary phase shift keying (BPSK), a quadrature phase shift keying(QPSK), an M-ary phase shift keying (PSK), an M-ary quadrature amplitudemodulation (QAM), and the like, and there is no limit of the methods.The micro constellation mapping means a separate constellation mappingmethod for the additional data signals.

As described above, in this embodiment of the present invention, sincethe additional data signals are contained in the pilot signal to betransmitted by various methods, hereinafter, a method of transmittingthe additional data signals by containing the additional data signals inthe pilot signals will be described.

=P _(d)

+r _(p)exp(−jθ _(p))P _(p)

  [Formula 5]

where, r_(p) and θ_(p) are values that are commonly contained in thepilot signals and represent an amplitude and a phase, respectively. Inother words, the r_(p) exp(−jθ_(p)) represents the additional datasymbol that the additional data bits are converted by the microconstellation mapping. A signals of the Formula 5 is converted into thetime domain signal by carrying out the Formula 2 and may be transmittedto the receiving end.

Signals in which the additional data signals, the pilot signals, and theuser data signals are contained are transmitted by a plurality ofsub-carriers.

According to this embodiment of the present invention, since thetransfer symbol, to which at least two constellation mapping methods areapplied, is preferably transmitted by a plurality of sub-carriers beingorthogonal to each other as described above, the transfer symbol can betransmitted by various methods.Hereinafter, for the illustrative convenience, a series of procedures ofmapping the data symbol, to which the constellation mapping is carriedout, to specific sub-carriers and of transmitting the mapped data symbolto the receiving end is called an OFDM transmitting data process. Sincethe OFDM transmitting data process includes a data processing operationcarried out in processing blocks following the S/P converter 240, it isobvious to those skilled in the art that the OFDM transmitting dataprocessing operation may use another communication device for theimprovement of the transmission quality.

Hereinafter, a method of commonly containing the additional data signalsin the user data signals to be transmitted according to the embodimentof the present invention will be described.

=r _(p)exp(−jθ _(p))P _(d)

+P _(p)

  [Formula 6]

where, r_(p) and θ_(p) are values commonly contained in the pilotsignals, and represent an amplitude and a phase, respectively.

When the additional data signals are contained in the user data signalsas expressed by the formula 6, there are advantages as follows. In acase of the pilot signals, there is a limit for the number of the pilotsignals, and the pilot signals are used in the equalization and thechannel estimation of the receiving end. In a case of using the formula5 to contain the additional data signals in the pilot signals, theequalization or the channel estimation may be difficult. Thus, when theadditional data signals are contained to the user data signals insteadof the pilot signals, this problem in the receiving end can be solved.Since it is preferred that the transfer symbol, to which at least twoconstellation mapping methods are applied, is transmitted by theplurality of sub-carriers being orthogonal to each other as describedabove, the transfer symbol is transmitted to the receiving end by theOFDM transmitting data process.

As mentioned above, in this embodiment, since the additional datasignals are contained in the data signal by various methods,hereinafter, a method of containing the additional data signals in thedata signals to be transmitted will be described.

=diag{r ₁exp(−jθ ₁),r ₂exp(−jθ ₂),Λ,r _(N) _(d) exp(−jθ _(N) _(d) )}P_(d)

+P _(p)

  [Formula 7]The above formula, different from the formulas 5 and 6, represents amethod of grouping the user data symbols to be contained in a singleOFDM symbol and transmitting different additional data signals in therespective groups. N_(d) indicates the number of the groups and r₁exp(−jθ₁) to r_(N) _(d) exp(−jθ_(N) _(d) ) indicate the additional datasignals to be contained in the groups to be transmitted.The diag{r₁ exp(−jθ₁),r₂ exp(−jθ₂),Λ,r_(N) _(d) exp(−jθ_(N) _(d) )}indicates a method in which the respective phases and amplitudes areapplied to the sub-carriers being allocated to the respective user datasymbols. In Formula 7, r_(x) and θ_(x) (x is an integer from 1 to N_(d))have identical values with respect to the sub-carriers belonging to asingle sub-carrier group, where the single sub-carrier group containsidentical additional data signals.Moreover, as described above, the additional data signals are mappedinto the specific additional data symbols by the micro constellationmapping. The diag{ } operation is an operation of converting a certainvector into a matrix, and the matrix has a diagonal vector component.If the quantity of the additional data signals to be transmitted to thereceiving end is great, it is preferred that, like the method expressedby the formula 7, the different additional data signals are contained inthe respective groups of the user data symbols.

Consequently, a new additional channel may be provided between thetransmitting end and the receiving end through the method oftransmitting the additional data signals by further containing theadditional data signals in the user data symbols.

Moreover, in this embodiment, in order to transmit the additional datasignals by containing the additional data in the additional datasignals, constellation information to modify the amplitude and the phaseon a constellation map is used.

The transmitting end according to this embodiment is characterized inthat control information with respect to the phase or the amplitudemodified by the micro constellation mapping is not transmitted. Thus,the receiving end receives signals from the transmitting end andestimates and removes the micro constellation mapping to recover thedata signals to which the macro constellation mapping is carried out.Hereinafter, operation of the receiving end will be described.

FIG. 4 is a view illustrating the receiving end to receive receivingsignals, containing additional data signal, according to this embodimentof the present invention. The receiving end according to this embodimentincludes a serial-to-parallel (S/P) converter 480 to convert a serialinput into a parallel output, an N-point fast Fourier transform (FFT)470, a demultiplexer (deMUX) 460 to distinguish data and pilots mixedaccording to a predetermined rule, a channel estimating and equalizer450 to estimate a channel using the pilots and to recover aconstellation coordinate on a constellation map of the data through theestimated channel, a parallel-to-serial (P/S) converter 440 to convert aparallel input into a serial output, a module 430 to generate aconstellation group from the equalized data signals and to estimate themicro constellation mapping of finding a micro constellation signal fromthe constellation group, a demapping module 420 to recover the microconstellation mapping of finding the data transmitted from the microconstellation signals to acquire the additional data, and a demappingmodule 410 to recover the macro constellation mapping to acquire theuser data.

The OFDM signal received through the channel firstly undergoes the S/Pconversion and the converted signal is converted into a signal in thefrequency domain through an FFT block. A channel of this convertedsignal is estimated through the pilots and the data signal is equalized.If the pilot signals are received to estimate the channel in a maximumlikelihood method, the following estimating value can be obtained.

$\begin{matrix}{{\begin{bmatrix}\hat{h} \\0\end{bmatrix} = {{{a^{H}\left( {F^{H}V_{P}^{H}V_{P}F} \right)}^{- 1}F^{H}V_{P}^{H}{\overset{\rho}{v}}_{R}^{P}\mspace{14mu}{{or}\begin{bmatrix}\hat{h} \\0\end{bmatrix}}} = {\left( {F^{H}V_{P}^{H}V_{P}F} \right)^{- 1}F^{H}V_{P}^{H}{\overset{\rho}{v}}_{R}^{P}}}}\mspace{11mu}} & \left\lbrack {{Formula}\mspace{14mu} 8} \right\rbrack\end{matrix}$

where, ‘a’ represents r_(p) exp(−jθ_(p)), ‘F’ represents a Fouriertransform matrix, and V_(p) is an diagonal matrix. When only the pilotcomponents transmitted from the transmitting end are selected to expressa vector of a length N (where non-pilot elements of the vector arefilled with ‘0’ (zero)), the vector of the length N becomes an diagonalelement of the V_(p).

represents a pilot component of a received signal vector

The first value in the formula 8 is an estimated value when theadditional data signals are contained in the pilot signals, and thesecond value is an estimated value when the additional data signals arecontained in the data signals. The estimated channel response isconverted into the frequency domain to find a channel value with respectto positions of the sub-carriers of the respective data symbols asexpressed by the following formula 9.

$\begin{matrix}{\hat{H} = {F\begin{bmatrix}\hat{h} \\0\end{bmatrix}}} & \left\lbrack {{Formula}\mspace{14mu} 9} \right\rbrack\end{matrix}$

When signals of the positions of the sub-carriers to transmit the datasymbols through the estimated channel are equalized, the followingformula 10 can be expressed. The formula 10 is an example of a case ofcontaining the additional data signals in the pilot signals andtransmitting the same.{circumflex over (v)} _(s)=(P _(d) ^(H) Ĥ ^(H) ĤP _(d))⁻¹ ĤP _(d)

=r _(p) ³exp(−jθ _(p))(P _(d) ^(H) H ^(H) HP _(d))⁻¹ HP _(d)

  [Formula 10]

where, H=Ĥ/a^(H), and

is a vector corresponding to data components in the received signalvector

When the additional data contained in the data components aretransmitted, additional information is expressed in the simple form likeformula 11.{circumflex over (v)} _(s) =r _(p)exp(−jθ _(p))(P _(d) ^(H) Ĥ ^(H) ĤP_(d))⁻¹ ĤP _(d)

  [Formula 11]

The constellation of the data signals estimated from the formulas 10 or11 takes a form rotated by a predetermined value according toadditionally contained data. Moreover, amplitude of the constellationcoordinates can be changed according to additionally contained data.FIG. 5 is a view illustrating a constellation map of data in which themacro constellation mapping is carried out by a binary phase shiftkeying (BPSK) and the micro constellation is carried out. FIG. 5illustrates a result when the amplitude of the additional data signal isset to 1 (one) and the phase thereof is set to 30 degrees.

In this embodiment, it is preferred that the channel estimation and theequalization are carried out in order for the correct demodulation ofthe receiving end. This embodiment proposes a method of estimating andrecovering an amplitude and a phase corresponding to respective datasymbols (the user data signals, the pilot signal, and the additionaldata signals that are transmitted by the transmitting end) receivedthrough the respective orthogonal sub-carriers. The data symbols,received through the respective sub-carriers, are data symbols that arereceived through a receiving antenna and are undergone by theserial-to-parallel conversion and the FFT conversion, and hereinafter,are referred to as ‘received symbols’. Consequently, the receivedsymbols in this embodiment are data symbols corresponding to transmittedsymbols to which two constellation mappings are applied in thetransmitting end, and two constellation demappings are carried out tothe received symbols so that the additional data signals and the userdata signals can be recovered.

As described above, the transmitting end in this embodiment does notprovide information about r_(p) and θ_(p) to the receiving end, and asknown through FIG. 5, since the receiving end receives signals differentfrom already known BPSK constellation, the receiving end is able toestimate the information about the micro constellation (r_(p) and θ_(p))without help of the transmitting end.

In a case as illustrated in FIG. 5, although the amplitude (namely,r_(p)=1) is not varied, since the phase is changed, the phase is rotatedin comparison to the conventional BPSK so that the rotated quantity canbe estimated. However, in order to estimate the rotated quantity, thereis a problem of knowing correct values of the respective data symbols.Thus, the module 430 to estimate the micro constellation mapping uses atechnique of finding the correct values of the respective receivedsymbols.Firstly, since information for the respective data is not known, theadded amplitude and phase (the micro constellation) must be obtained bygrouping the respective data and mapping the same in the constellation(the macro constellation) of the original data according to theconstellation coordinates gathered on the constellation map. Since asingle OFDM symbol contains a plurality of data symbols, theconstellations with respect to a plurality of received symbols (namely,amplitudes and phases corresponding to the respective received symbols)can be acquired at once, and these plural constellations are comparedwith the macro constellation so that the information about the microconstellation can be estimated.

Hereinafter, an example of algorithms of estimating the amplitudes andthe phases added by the micro constellation mapping will be described.

1. Allocating a single sample to a certain group

2. Updating centroids of K groups using the following formula. This is aprocedure of calculating centers of gravity of the respective groups.

$\begin{matrix}{m_{j} = {\frac{1}{N_{j}}{\sum\limits_{P = 0}^{N_{j} - 1}d_{P}^{j}}}} & \left\lbrack {{Formula}\mspace{14mu} 12} \right\rbrack\end{matrix}$

where, m_(j) is a centroid of a group, N_(j) is the number of samplesbelonged to a corresponding group, and d_(p) ^(j) is a sample pthbelonged to jth group.

3. By taking the number of data belonging to the respective groups intoconsideration, a weight coefficient is determined and K centroids arerenewed again on the basis of the determined weight coefficient. Inother words, the center of gravity is renewed to be mostly similar tothe respective constellation points.

$\begin{matrix}{J = {\frac{\sum\limits_{k = 1}^{K}{w_{k}\left( {X_{k} - m_{k}} \right)}^{2}}{\sum\limits_{k = 1}^{K}w_{k}} = \frac{\sum\limits_{k = 1}^{K}{w_{k}\left( {{X_{1}{\exp\left( {{j\left( {k - 1} \right)}\theta_{X}} \right)}} - m_{k}} \right)}^{2}}{\sum\limits_{k = 1}^{K}w_{k}}}} & \left\lbrack {{Formula}\mspace{14mu} 13} \right\rbrack \\{\mspace{79mu}{\frac{\partial J}{\partial X_{1}} = \frac{\sum\limits_{k = 1}^{K}{2{w_{k}\left( {X_{1} - {m_{k}{\exp\left( {{- {j\left( {k - 1} \right)}}\theta_{X}} \right)}}} \right)}}}{\sum\limits_{k = 1}^{K}w_{k}}}} & \left\lbrack {{Formula}\mspace{14mu} 14} \right\rbrack \\{\mspace{79mu}{X_{1} = \frac{\sum\limits_{k = 1}^{K}{w_{k}m_{k}{\exp\left( {{- {j\left( {k - 1} \right)}}\theta_{X}} \right)}}}{\sum\limits_{k = 1}^{K}w_{k}}}} & \left\lbrack {{Formula}\mspace{14mu} 15} \right\rbrack\end{matrix}$

where, X_(k) is kth macro constellation point, and W_(k) is a weightcoefficient and equal to N_(j). θ_(x) is an angular rotation valuebetween the constellation coordinates. θ_(x) is, for example, 90 degreesin the M-ary QAM and 180 degrees in the BPSK.

4. When there are unallocated samples, one of the unallocated samples isselected to allocate the selected one to the nearest group of the Kgroups.

5. The procedures 2, 3, and 4 are repeated with respect to the newlyallocated sample.

The transmitting end according to this embodiment additionally transmitsthe additional data signals by carrying out the micro constellationmapping, and the receiving end according to this embodimentspontaneously estimates information about the micro constellationmapping to recover the additional data signals transmitted by the microconstellation mapping and the user data signals transmitted by the macroconstellation mapping. Hereinafter, a method of determining theconstellation coordinate of the micro constellation mapping used in thetransmitting end and the receiving end will be described.

The coordinate of the micro constellation must be within a range ofdistinguishing the coordinate of the macro constellation. FIG. 6Aillustrates a phase range that the micro constellation coordinate mayhave when the macro constellation mapping is the BPSK. Referencenumerals 600 and 630 in the drawing represent the macro constellationcoordinates mapped by the macro constellation mapping. Moreover,reference numerals 601 and 631 are assigned to the constellationcoordinates in which the macro constellation coordinates are rotated bythe micro constellation mapping.

A left-side of FIG. 6A indicates constellation coordinates rotated bythe micro constellation. The transmitting end rotates the constellationcoordinates 600 and 630 in which the additional data signal are notcontained. By the rotating operation, the constellation coordinates 601and 631 are generated.A right-side of FIG. 6A illustrates a concept that the receiving endrecovers the constellation coordinates. The receiving end acquires theadditional data signals through the constellation coordinates 601 and631 with respect to the transfer signals in which the additional datasignals are contained and eliminates the rotated components due to themicro constellation mapping to recover the constellation coordinates 600and 630 due to the original macro constellation mapping.If the receiving end fixes the direction of recovering the constellationcoordinates to the clockwise direction or the counterclockwisedirection, when the macro constellation mapping is the BPSK, thereceiving end can correctly recover the constellation coordinatesalthough the phase is rotated by 0 degrees to 180 degrees by the microconstellation mapping.

FIG. 6B illustrates a range of values that the micro constellationcoordinates may have when the macro constellation mapping is the M-aryquadrature amplitude modulation (QAM). A reference numeral 640 in thedrawing indicates one of the macro constellation coordinates mapped bythe macro constellation mapping in the M-ary QAM method, and referencenumeral 641 indicates constellation coordinates in which the macroconstellation coordinates 640 are rotated by the micro constellationmapping. As illustrated in the left-side of FIG. 6B, when a usual M-aryQAM type macro constellation coordinate is rotated by 0 degrees to 90degrees, the receiving end can correctly receive the same withoutadditional control information. The receiving end can acquire theconstellation coordinates, the phases of which are rotated by the microconstellation mapping, and can recover the constellation coordinatesinto the conventional macro constellation coordinates. In other words,if the receiving end fixes the direction of recovering the constellationcoordinates to the clockwise direction or the counterclockwisedirection, when the macro constellation mapping is the M-ary QAM, thereceiving end can correctly recover the constellation coordinatesalthough the phases are rotated by 0 degrees to 90 degrees by the microconstellation mapping.

Consequently, when the macro constellation mapping is the BPSK, thechange of the phases due to the micro constellation mapping must be 0degrees to 180 degrees. Moreover, when the macro constellation mappingis the M-ary QAM, the change of the phases caused by the microconstellation mapping must be 0 degrees to 90 degrees.

As described above, since the range of the variation of the phases inthe micro constellation mapping is restricted to a predetermined value,the micro constellation mapping can be determined by various methodswithin the range of the phase variation. By changing the microconstellation mapping, the conversion relationship between theadditional data bits and the data symbols due to the same is determined.Such micro constellation mapping is preferably determined by acommunication circumstance such as a permissible error ratio.

FIG. 7 is a view illustrating a result that the micro constellationcoordinate is generated when the macro constellation mapping is theBPSK. FIG. 7( a) illustrates an example of using μ-BPSK as the microconstellation mapping when the macro constellation mapping is the BPSK,FIG. 7( b) illustrates an example of using μ-QPSK as the microconstellation mapping when the macro constellation mapping is the BPSK,and FIG. 7( c) illustrates an example of using μ-8 PSK as the microconstellation mapping when the macro constellation mapping is the BPSK.

As described above, when the macro constellation mapping is the BPSK,the phase rotation due to the micro constellation mapping is restrictedto 0 degrees to 180 degrees. The μ-BPSK means a method of selecting twophase values between 0 degrees to 180 degrees, for example, 45 degreesand 135 degrees to transmit the additional data. Since the constellationcoordinate due to the macro constellation mapping is identical to areference numeral 700, a constellation coordinate indicated by areference numeral 701 is obtained when a phase rotation of 45 degrees isapplied, and a constellation coordinate indicated by a reference numeral702 is obtained when a phase rotation of 135 degrees is applied. If theμ-BPSK as the micro constellation mapping is used between thetransmitting end and the receiving end, a transmitting end per group, towhich the micro constellation mapping is applied, can provide 1 (one)additional data bit through the micro constellation mapping. The μ-QPSKmeans a method of selecting four phase values from 0 degrees to 180degrees to transmit the additional data.In FIG. 7( b) illustrating an example of the μ-QPSK, a reference numeral730 is assigned to a constellation coordinate due to the macroconstellation mapping, and reference numerals 731, 732, 733, and 734 areassigned to micro constellation coordinates due to the phase rotation.Moreover, the μ-8 PSK means a method of selecting eight phase valuesfrom 0 degrees to 180 degrees to transmit the additional data.In FIG. 7( c) illustrating an example of the μ-8 PSK, a referencenumeral 760 is assigned to a constellation coordinate due to the macroconstellation mapping, and reference numerals 761, 762, 763, 764, 765,766, 766, and 768 are assigned to micro constellation coordinates due tothe phase rotation. Since the above-mentioned micro constellationmapping is only an example of the micro constellation mapping accordingto the present invention, various micro constellation mappings areenabled by a phase conversion or an amplitude conversion according tothe micro constellation.

FIG. 8 is a view illustrating a result that the micro constellationcoordinate is generated when the macro constellation mapping is theM-ary QAM. FIG. 8( a) illustrates an example of using μ-BPSK as themicro constellation mapping when the macro constellation mapping is theM-ary QAM, FIG. 8( b) illustrates an example of using μ-QPSK as themicro constellation mapping when the macro constellation mapping is theM-ary QAM, and FIG. 8( c) illustrates an example of using μ-8 PSK as themicro constellation mapping when the macro constellation mapping is theM-ary QAM.

As described above, when the macro constellation mapping is the M-aryQAM, the phase rotation due to the micro constellation mapping isrestricted to 0 degrees to 90 degrees. The μ-BPSK means a method ofselecting two phase values between 0 degrees to 90 degrees, for example,30 degrees and 60 degrees to transmit the additional data. Since theconstellation coordinate due to the macro constellation mapping isidentical to a reference numeral 800, a constellation coordinateindicated by a reference numeral 801 is obtained when a phase rotationof 30 degrees is applied, and a constellation coordinate indicated by areference numeral 802 is obtained when a phase rotation of 60 degrees isapplied.If the μ-BPSK as the micro constellation mapping is used between thetransmitting end and the receiving end, a transmitting end per group, towhich the micro constellation mapping is applied, can provide 1 (one)additional data bit in the micro constellation mapping. The μ-QPSK meansa method of selecting four phase values from 0 degrees to 90 degrees totransmit the additional data.In FIG. 8( b) illustrating an example of the μ-QPSK, a reference numeral830 is assigned to a constellation coordinate due to the macroconstellation mapping, and reference numerals 831, 832, 833, and 834 areassigned to micro constellation coordinates due to the phase rotation.Moreover, the μ-8 PSK means a method of selecting eight phase valuesfrom 0 degrees to 90 degrees to transmit the additional data.In FIG. 8( c) illustrating an example of the μ-8 PSK, a referencenumeral 860 is assigned to a constellation coordinate due to the macroconstellation mapping, and reference numerals 861, 862, 863, 864, 865,866, 866, and 868 are assigned to micro constellation coordinates due tothe phase rotation.

FIG. 9 is a view illustrating a concept of a method of transmitting databy containing additional data in the data according to the embodiment ofthe present invention. As illustrated in FIG. 9, identical additionaldata can be contained in the conventional pilot signals to betransmitted, and identical additional data can be contained in theconventional data signals to be transmitted. Moreover, the additionaldata are differently contained in respective specific sub-carriers andare transmitted.

FIG. 10 is a view illustrating a maximum value of the additional datacontained in the pilot signals to be transmitted in the embodiment ofthe present invention. When the OFDM symbols are transmitted by 1024sub-carriers, the quantity of the additional data to be transmittedaccording to a channel circumstance is illustrated in the drawing.

FIG. 11 is a view illustrating an error rate with respect to theadditional data when the additional data is contained in the pilotsignals to be transmitted in the embodiment of the present invention.When the OFDM symbols are transmitted by 1024 sub-carriers, a bit errorrate (BER) according to a channel circumstance is illustrated in thedrawing.

FIG. 12 is a view illustrating an error rate of the phase estimationwith respect to the micro constellation signal when the additional datais contained in the pilot signals to be transmitted in the embodiment ofthe present invention. When the OFDM symbols are transmitted by 1024sub-carriers, the error ratio of the phase estimation with respect tothe micro constellation signal according to a channel circumstance isillustrated in the drawing.

FIG. 13 is a view illustrating an error rate with respect to theadditional data when the additional data is contained in the datasignals to be transmitted in the embodiment of the present invention.When the OFDM symbols are transmitted by 1024 sub-carriers, the BERaccording to a channel circumstance is illustrated in the drawing.

FIG. 14 is a view illustrating an error ratio of the phase estimationwith respect to the micro constellation signals when the additional datais contained in the data signals to be transmitted in the embodiment ofthe present invention. When the OFDM symbols are transmitted by 1024sub-carriers, the error ratio of the phase estimation with respect tothe micro constellation signal according to a channel circumstance isillustrated in the drawing.

Hereinafter, as one of various methods of using the micro constellationmapping proposed in the above-mentioned first embodiment, a method oftransmitting and receiving information about the PAPR by the microconstellation mapping will be described.

Embodiment 2

In the second embodiment of the present invention, a method of reducingthe PAPR in the OFDM communication system is provided.

In the second embodiment, a specific phase shift is carried out to agroup of the sub-carriers containing at least two sub-carriers in orderto reduce the PAPR. In this embodiment, a phase component is multipliedto generate the phase shift so that the PAPR is reduced but neitheradditional sub-carrier is allocated to transmit additional informationabout the phase component nor power is increased.

The second embodiment is characterized in that respective transfersymbols, in which the phase shift is performed, contain the additionalinformation to indicate the phase component and are transmitted. In thisembodiment, in order to distinguish the additional information and thephase component from each other, phases of the symbols transmitted bythe group of the sub-carriers are controlled.

FIG. 15 is a view illustrating an example of an OFDM signal transmittingend to reduce PAPR according to an embodiment of the present invention.In FIG. 15,

represent a data symbol transmitted by the transmitting end. The datasymbols are generated by the macro constellation mapping such as theBPSK, QPSK, the M-ary PSK, the M-ary QAM, and the like. Moreover, aphase identifier in FIG. 15 is identifying information representing aPAPR code that is applied to a specific sub-carrier group. The PAPR codeis multiplied to the sub-carrier group to indicate data containing aphase component of reducing the PAPR of the OFDM signals. Since thisembodiment uses modulated data to control the phases of transfer signalsthat are transmitted by the specific sub-carrier group, the modulateddata has no restriction of own kind when the modulated data control thephases of the transfer signals. For example, the modulated data may bethe phase components to rotate the phases of the transfer signals thatare transmitted by the specific sub-carrier group.

Hereinafter, operation of the transmitting end will be described. Thedata symbols transmitted by the transmitting end are converted intoparallel signals by a serial-to-parallel (S/P) converter 1501. The PAPRcode of reducing the PAPR is applied to the parallel signals by phasemappers 1502, 1503, and 1504, and the parallel signals containadditional information of indicating the PAPR code. The signalscontaining the PAPR code and the additional information are convertedinto the OFDM signals by an IFFT module 1505, a parallel-to-serial (P/S)converter 1506, and a cyclic prefix inserter 1507.

The transmitting end according to this embodiment applies the PAPR codeto the sub-carrier group through the phase mappers 1502, 1503, and 1504.Moreover, the phase mappers 1502, 1503, and 1504 use a microconstellation mapping distinguished from the conventional macroconstellation mapping for the user data signals and the pilot signals tocontain the additional information of identifying the PAPR code by thereceiving end.

FIG. 16 is a view illustrating an example of a phase mapper 1502according to this embodiment of the present invention. The phase mapper1502 includes a macro phase selector 1610 to apply the PAPR code to thesub-carrier group, a micro phase selector 1620 to contain the additionalinformation in which the receiving end identifies the PAPR code withoutadditional control information, and at least one multiplier 1630 tomultiply a macro phase or a micro phase to the transfer symbols.Hereinafter, operation of the phase mappers will be described withreference to FIG. 16.

The phase mappers 1502, 1503, and 1504 apply the PAPR code to any one ofat least one sub-carrier group. When the sub-carrier group is called k,s_(k) ^(i) represents an ith transfer symbol (a data symbol or a pilotsymbol) of a kth group, and C_(k) is an identifier representing the PAPRcode to be applied to the kth sub-carrier group. Since φ_(k) ^(m)represents the PAPR code with respect to the kth sub-carrier groupindicated by C_(k), φ_(k) ^(m) represents a phase rotated by the PAPRcode. φ_(k) ^(u) represents additional information for informing a valueof φ_(k) ^(m) to the receiving end, namely, the phase due to the microconstellation mapping. Consequently, the transfer symbol undergoes phaseshifts twice by φ_(k) ^(u) and φ_(k) ^(m). In other words, φ_(k) ^(m)causes the phase shift for the reduction of the PAPR, and φ_(k) ^(u)causes the phase shift for indicating information about φ_(k) ^(m). Inthe present invention, the phases of the transfer signals are modifiedagain using additional modulated data of indicating the modulated datato reduce the PAPR. The modulated data to modify the phases of thetransfer signals again indicate data of controlling the phases of thetransfer signals, for example, the data may be phase components tochange the phases with respect to a specific sub-carrier group.

As described above, in this embodiment, the phases are changed twice,and the transmitted signals through the sub-carrier group are expressedby the following formula.u _(k) ^(i)=exp(j(φ_(k) ^(m)+φ_(k) ^(u)))s _(k) ^(i)  [Formula 16]

As described above, in order for the receiving end to recover thesignals in which the phase shifts occur twice, a predetermined conditionmust be satisfied. The transfer symbol has a specific phase value due tothe macro constellation mapping and undergoes the phase shifts twice byφ_(k) ^(u) and φ_(k) ^(m). Thus, in order for the receiving end tocorrectly receive, constellation coordinates caused by the macroconstellation mapping must not changed by the phase shift due to φ_(k)^(m). The constellation coordinates represent overall coordinates of thetransfer symbols marked on the constellation map. FIG. 17A is a viewillustrating a method of selecting a value of φ_(k) ^(m) when the macroconstellation mapping is the M-ary QAM. In this embodiment, in order forthe receiving end to correctly receive, as illustrated in FIG. 17A, theconstellation coordinates must not changed by the phase shift due toφ_(k) ^(m). Thus, when the macro constellation mapping is the M-ary QAM,φ_(k) ^(m) is determined by the following formula.

$\begin{matrix}{\phi_{k}^{m} = \left\{ {0,\frac{\pi}{2},\pi,\frac{3\;\pi}{2}} \right\}} & \left\lbrack {{Formula}\mspace{14mu} 17} \right\rbrack\end{matrix}$

In other words, when the macro constellation mapping is the M-ary QAM,φ_(k) ^(m) may be selected by one of the phases contained in the formula17 to be used. As described above, when φ_(k) ^(m) is one of 0 degreephase, 90 degree phase, 180 degree phase, and 270 degree phase, overallarrangement of the constellation coordinate due to the M-ary QAM is notchanged. If all phases expressed by the formula 17 are used, the phaseidentifier C_(k) to identify φ_(k) ^(m) may be expressed by 2-bitinformation. moreover, when {0, π} is used from the phases expressed bythe formula 17, the phase identifier C_(k) to identify φ_(k) ^(m) may beexpressed by 1-bit information.

FIG. 17B is a view illustrating a method of selecting a value of φ_(k)^(m) when the macro constellation mapping is the BPSK. In thisembodiment, in order for the receiving end to correctly receive, asillustrated in FIG. 17B, the constellation coordinates must not changedby the phase shift due to φ_(k) ^(m). Thus, when the macro constellationmapping is the BPSK, φ_(k) ^(m) is determined by the following formula.φ_(k) ^(m)={0,π}  [Formula 18]

In other words, when the macro constellation mapping is the BPSK, φ_(k)^(m) may use the phases contained in the formula 18. If, when the phasesexpressed by the formula 18 are used, the phase identifier Ck toidentify φ_(k) ^(m) may be expressed by 1-bit information.

As described above, when φ_(k) ^(m) is determined, the receiving enddetermined the phase shift due to φ_(k) ^(u). In other words, since themacro constellation mapping is determined by the transmitting end andthe receiving end, if information in which φ_(k) ^(u) indicates whichφ_(k) ^(m) is already notified to the transmitting end and the receivingend, the receiving end can determine φ_(k) ^(m) the phase shift due toφ_(k) ^(u).

Hereinafter, the transmitting end according to an embodiment of thepresent invention will be described.

FIG. 18 illustrates configuration of the receiving end according to theembodiment of the present invention. The receiving end according to thisembodiment includes a cyclic prefix remover 1807 to remove a cyclicprefix inserted by the transmitting end, a serial-to-parallel (S/P)converter 1806 to output a serially inputted sequence in the form of aparallel sequence, an FFT module 1805 to perform a FFT operation, atleast one phase demapper 1802, 1803, or 1804 to remove a PAPR codeapplied to reduce the PAPR, and a parallel-to-serial (P/A) converter1801 to output an inputted parallel vector in the form of a serialvector. In the drawing,

represents a time domain signal vector of the OFDM signal received bythe receiver, and

represents the recovered data symbols. Hereinafter, operation of thereceiving end will be described.

The signal received by the receiving end is converted into the frequencydomain signal after removing the cyclic prefix contained in the receivedsignal. The received signal, since the PAPR code to reduce the PAPR isapplied to the respective sub-carrier groups, must carry out anoperation of removing the PAPR code in order to correctly demodulate thedata. The operation of removing the PAPR code is carried out by one ofthe phase demappers. In other words, the phase demapper 1802 carries outthe removal of the PAPR code with respect to the specific sub-carriergroups. FIG. 19A is a view illustrating an example of the phase demapper1802 according to the embodiment of the present invention. The phasedemapper 1802 includes a micro constellation estimator 1930 to estimatea phase due to the micro constellation mapping and to output the phaseID, a macro phase selector 1910 to select a PAPR code of reducing thePAPR according to information about the phase ID, a micro phase selector1920 to select additional information representing the PAPR code, and atleast one multiplier 1940 to multiply the outputs from the selectors1910 and 1920 in reverse process (by changing plus/minus signs) than thecase of the transmitting end according to this embodiment to remove theadditional information and the PAPR code.

The micro constellation estimator 1930 is a module to estimateinformation about φ_(k) ^(u) of representing φ_(k) ^(m) for thereduction of the PAPR. As described above, the macro constellationmapping is already determined by the transmitting end and the receivingend, and the macro constellation coordinates due to the macroconstellation mapping are not changed by φ_(k) ^(m). Thus, the microconstellation estimator 1930 can correctly estimate φ_(k) ^(u). Themicro constellation estimator 1930 outputs the phase ID C_(k) to themacro phase selector 1910 and the micro phase selector 1920 according toφ_(k) ^(u) such that the phase selectors 1910 and 1920 acquire φ_(k)^(m) and φ_(k) ^(u) that are used in the transmitting end according tothis embodiment. The phase selectors 1910 and 1920, according to theinformation about the phase ID C_(k), output φ_(k) ^(m) and φ_(k) ^(u)to the multiplier 1940 to remove the components of φ_(k) ^(m) and φ_(k)^(u).

Since various algorithms can be used to estimate φ_(k) ^(u), data to beobtained to estimate φ_(k) ^(u) can be obtained by the followingformulas.

$\begin{matrix}{{X^{C}(\phi)} = \left\{ {{{\exp\left( {j\;\phi} \right)}X_{0}},{{\exp\left( {j\left( {\frac{\pi}{2} - \phi} \right)} \right)}X_{0}},{{\exp\left( {j\left( {\frac{2\;\pi}{2} - \phi} \right)} \right)}X_{0}},{{\exp\left( {j\left( {\frac{3\;\pi}{2} - \phi} \right)} \right)}X_{0}}} \right\}} & \left\lbrack {{Formula}\mspace{14mu} 19} \right\rbrack \\{\mspace{79mu}{{J\left( {u_{k}^{i},{X^{C}(\phi)}} \right)} = {\min\limits_{{n = 0},1,2,3}{{{\exp\left( {j\left( {\frac{n\;\pi}{2} + \phi} \right)} \right)} - u_{k}^{i}}}^{2}}}} & \left\lbrack {{Formula}\mspace{14mu} 20} \right\rbrack \\{\mspace{79mu}{{\hat{\phi}}_{k}^{\prime\; u} = {\arg\;{\min\limits_{{\phi \in_{-}^{-}0},{\varphi^{\mu}}_{-}^{-}}{\sum\limits_{i = 1}^{N_{k}}{J\left( {u_{k}^{i},{X^{C}(\phi)}} \right)}}}}}} & \left\lbrack {{Formula}\mspace{14mu} 21} \right\rbrack\end{matrix}$

In the above formulas, φ^(u) is a maximal value of a phase range thatthe signal may have in the micro constellation method. Using a valueobtained from the formula 21, C_(k) is estimated and the correspondingφ_(k) ^(m) is removed from the respective signals.

FIG. 19B is a view illustrating another example of the phase demapper1802 according to the embodiment of the present invention. The phasedemapper 1802 in FIG. 19B includes a micro constellation estimator 1980having the same algorithm as that of the phase demapper in FIG. 19A.However, the micro constellation estimator 1980 outputs the phase IDC_(k) to a macro phase selector 1960 and outputs φ_(k) ^(u) to at leastone multiplier 1970. The phase demapper, when the micro constellationestimator has an error to determine the phase ID Ck, can prevent theerror from being applied to φ_(k) ^(u).

Hereinafter, when the macro constellation mapping is the BPSK and φ_(k)^(m)={0,π}, a method of calculating the phase in the transmitting endand the receiving end will be described. Since φ_(k) ^(m) can bedistinguished by 1-bit phase ID C_(k), φ_(k) ^(m) is determined as ‘0’(zero) and φ_(k) ^(u) is determined as ‘0’ (zero) when C_(k) is ‘0’(zero) with respect to a specific sub-carrier group k, and φ_(k) ^(m) isdetermined as ‘π’ (pi) and φ_(k) ^(u) is determined as ‘π/6’ (pi/6) whenC_(k) is ‘1’ (one). If the transmitting end according to this embodimentdetermines φ_(k) ^(m) as ‘0’ (zero) with respect to the specificsub-carrier group k in order to reduce the PAPR, φ_(k) ^(u) becomes ‘0’(zero) and a phase of ‘0’ (zero) is applied to the original BPSK symbol.Since there is additional phase component other than the conventionalBPSK constellation coordinates, the transmitting end according to thisembodiment estimates φ_(k) ^(u) as ‘0’ (zero) and determines C_(k) as‘0’ (zero) according to the value 0 (zero) of φ_(k) ^(u). If the signalsare received by the phase demapper in FIG. 19A, C_(k) having a value ‘0’(zero) is outputted to the macro phase selector 1910 and the micro phaseselector 1920 to remove the components of φ_(k) ^(u)(=‘0’ (zero)) andφ_(k) ^(m) (=‘0’ (zero)).

Moreover, when φ_(k) ^(m) is determined as ‘π’ (pi) with respect to thespecific sub-carrier group k in order for the transmitting end accordingto this embodiment to reduce the PAPR, φ_(k) ^(u) becomes ‘π/6’ so thata phase of ‘7π/6’ is applied to the original BPSK symbol. Since there isadditional phase component as much as ‘π/6’ in comparison to theconventional BPSK constellation coordinates, the transmitting endaccording to this embodiment estimates φ_(k) ^(u) as ‘π/6’ and Ck as ‘1’(one) according to the determination for φ_(k) ^(u) as ‘π/6’. If whenthe signals are received by the phase demapper in FIG. 19A, Ck having avalue ‘1’ (one) is outputted to the macro phase selector 1910 and themicro phase selector 1920 to remove the components of φ_(k) ^(u)(=‘π/6’) and φ_(k) ^(m) (=‘π/6’).

FIG. 20 is a view illustrating performance when the data transmittingand receiving method according to an embodiment of the present inventionis used. FIG. 20 illustrates the performance to which the reduction ofthe PAPR is not applied. FIG. 20 also illustrates the performance towhich the sub-carriers are grouped into 2, 3, and 4 sub-carrier groupsto apply the PAPR code. FIG. 20 relates to a performance when a singleOFDM symbol comprises 256 subcarrier. The PAPR performance isrepresented by complementary cumulative distribution function (CCDF) andFIG. 20 illustrates possibility in excess of a specific PAPR value.

FIG. 21 is another view illustrating the performance when a datatransmitting and receiving method according to the embodiment of thepresent invention is used. FIG. 21 illustrates the performance to whichthe reduction of the PAPR is not applied. FIG. 21 also illustrates theperformance to which the sub-carriers are grouped into 2, 3, and 4sub-carrier groups to apply the PAPR code. FIG. 20 relates to aperformance when a single OFDM symbol comprises 1024 subcarrier.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

INDUSTRIAL APPLICABILITY

According to the present invention, the following advantage can beobtained.

According to the present invention, since additional data channels otherthan the conventional data channels are generated, the effectiveness ofthe broadband of the conventional communication system can be increased.

What is claimed is:
 1. A method of transmitting signals to a receiver bya transmitter, the method comprising: transmitting a time domain signalto the receiver, wherein: at least one first information bit ismodulated using a first constellation mapping, resulting in at least onefirst modulated symbol; at least one second information bit is modulatedusing a second constellation mapping, resulting in at least one secondmodulated symbol; at least one third information bit is modulated usinga third constellation mapping, resulting in at least one third modulatedsymbol; the at least one second modulated symbol, which is a result ofthe modulation of the at least one second information bit, is combinedwith the at least one third modulated symbol, which is a result of themodulated of the at least one third information bit; the time domainsignal is generated from the at least one first modulated symbol, whichis not combined with the at least one third modulated symbol, and the atleast one second modulated symbol which is combined with the at leastone third modulated symbol; and the second constellation mapping isdifferent from the third constellation mapping.
 2. The method of claim1, wherein the at least one second modulated symbol and the at least onethird modulated symbol are transmitted through a same subcarrier.
 3. Themethod of claim 1, wherein the at least one first modulated symbol islocated before the at least one second modulated symbol.
 4. An apparatusfor transmitting signals to a receiver, the apparatus comprising: afirst constellation mapper modulating at least one first informationbit, resulting in at least one first modulated symbol; a secondconstellation mapper modulating at least one second information bit,resulting in at least one second modulated symbol; a third constellationmapper modulating at least one third information bit, resulting in atleast one third modulated symbol; wherein the at least one secondmodulated symbol, which is a result of the modulation of the at leastone second information bit, is combined with the at least one thirdmodulated symbol, which is a result of the modulated of the at least onethird information bit; and a transmitter transmitting a time domainsignal to the receiver, wherein the time domain signal is generated fromthe at least one first modulated symbol, which is not combined with theat least one third modulated symbol, and the at least one secondmodulated symbol which is combined with the at least one third modulatedsymbol, and wherein the second constellation mapping is different fromthe third constellation mapping.
 5. The apparatus of claim 4, whereinthe at least one second modulated symbol and the at least one thirdmodulated symbol are transmitted through a same subcarrier.
 6. Theapparatus of claim 4, wherein the at least one first modulated symbol islocated before the at least one second modulated symbol.